My fish are developing a cotton like substance on their bodies. I have had this problem befor and I have treated it with methylene blue. I have been free of this disease for some time and I introduced three new fish to the tank over Xmas, could this be the problem?

Check your water chemistry and treat all the fish for fungus. My choice would be Pimafix. Directions are on the bottle and you can get it at almost any store that sells aquarium products. If fungus keeps coming back you might need to tear down the tank, disinfect and start over.

Check your water chemistry and do a water change accordingly. You can add your usual water conditioner and also add aquarium salt....1 TBS per 5 gallons of water. You can add the pimafix then tomorrow.